Aug 22 (Reuters) -Spot basis bids for corn shipped by barge to the U.S. Gulf Coast strengthened further on Thursday, while FOB offers were steady to higher.

* Traders focused on increasing export demand for U.S. grain and concerns over low water levels on the Mississippi River slowing barge shipments of export-bound crops. A lack of rain is expected to keep river levels low heading into September as farmers start to harvest corn and soy.

* Exporters sold 110,490 metric tons of U.S. corn to Mexico and 132,000 metric tons to unknown buyers for delivery in 2024/25, the U.S. Department of Agriculture said in its daily reporting system.

* USDA also reported private sales of 198,000 metric tons of U.S. soybeans to China and 105,000 metric tons of U.S. soymeal to Vietnam. It was the fourth consecutive day that USDA confirmed soy sales to top-importer China in its daily system.

* Brokers said Chinese demand is lagging for U.S. corn and soybeans despite the sales.

* The USDA reported net cancellations of 43,700 tons of old-crop soybean export sales in the week ended Aug 15. New-crop weekly sales of 1.677 million tons exceeded trade estimates for up to 1.35 million tons.

* Net old-crop U.S. corn export sales of 119,100 tons in the week ended Aug. 15 were in line with analysts' estimates, while new-crop sales of 1.291 million tons topped trade expectations for up to 1.025 million tons. EXP/CORN

* CIF Gulf corn barges loaded in August were bid 3 cents higher at 68 cents over CBOT September CU24 futures. September corn barges were bid 4 cents higher at 80 cents over futures.

* FOB Gulf September corn export premiums were flat at about 92 cents over CBOT September corn futures. October export premiums jumped 10 cents to about 91 cents over CBOT December futures CZ24.

* CIF Gulf soybean barges loaded in August were up 1 cent at about 66 cents over CBOT November SX24 soybean futures. September soybean barge bids stayed unchanged at 64 cents over futures.

* FOB soy export premiums for early September loading at the Gulf were flat at about 110 cents over November futures, while last-half September shipments were steady at about 90 cents over futures.

Reporting by Tom Polansek; Editing by Jamie Freed

For displays of CIF basis, click on the codes in brackets: U.S. CIF Gulf soybeans GRYM U.S. CIF Gulf corn GRYN U.S. CIF Gulf SRW wheat GRYO U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets: U.S. FOB Gulf corn GRZC U.S. FOB Gulf soybeans GRZD U.S. FOB Gulf SRW wheat GRZE U.S. FOB Gulf HRW wheat GRZF LINKS Corn prices page: cpurl://apps.cp./cms/?pageid=corn-cash-market
Wheat prices page: cpurl://apps.cp./cms/?pageid=wheat-cash-market
U.S. barge freight BG/US
U.S. export sales estimates USDA/EST
U.S. grain export summary GRA/U
Brazil soybean export prices SYBS
Brazil corn export prices SYBX
Argentina grain prices GRA/ARG
Russia grain prices GRA/RU